1. Field of the Invention
This invention relates to an apparatus and method for harvesting and collecting aquatic plant biomass, and more particularly, to a system and method for harvesting and collecting attached algal communities or algal turf whereby water is utilized to transport algal biomass to a central collection location.
2. Description of the Background Art
For over one hundred years, government agencies and private entities have been attempting to design and develop strategies for harvesting aquatic plants. Initially, research efforts were directed at removal of aquatic plants from open water systems. Then, during the mid nineteen seventies, as researchers began to investigate the use of aquatic plants in water treatment, investigation began into harvest systems for use in man-made treatment systems.
In natural open water systems, the need to harvest aquatic plants is driven largely by the need to remove nuisance vegetation with capture of nutrient pollutants bound into plant tissue largely a secondary consideration. In constructed water treatment systems, harvesting of aquatic plants is necessary not only to gather plant biomass as a xe2x80x9ccropxe2x80x9d but also to remove plant tissue and attendant nutrient pollutants and maintain the overall health of the system.
Requisite to the function of many constructed water treatment systems is the cultivation of aquatic plants such as water hyacinth, duckweed or attached algal communities. The concept of artificial algae systems or Algal Turf Scrubbers (hereinafter xe2x80x9cATSxe2x80x9d) was first developed to permit nutrient management within aquaria-type facilities in which organisms, such as reef corals, which rely upon very low nutrient levels, could be sustained and cultivated. An ATS consists of a natural, mixed assemblage of attached periphyton, microalgae and bacteria which colonise a water floway, usually inclined, over which wastewater or nutrient rich water flows.
ATS are cultured communities of attached or benthic algae that can be used to manage water quality or to scrub a variety of nutrients or contaminants from marine, estuarine, and fresh water. ATS are complex algal communities and, as such, do not demonstrate the sensitivities and instabilities characteristic of monocultures of algae. See Adey, W. H., C. Luckett, and K. Jensen. 1993. xe2x80x9cPhosphorus removal from natural waters using controlled algal productionxe2x80x9d. Restoration Ecology. March 1993: 29-39.
It was discovered that when accompanied by extensive natural energies, such as currents or wave oscillations, algal communities within an ATS could sustain significant levels of productivity. Subsequently, it was suggested that algal communities could be supported within an engineered system to reduce nutrients, particularly phosphorus, from large volumes of nutrient enriched surface waters, such as wastewater and non-point sources (NPS). Today, ATS systems are used in thousands of aquaria, including a number of large-scale cultivation units (up to 1 million gallons). Studies in maximizing production of algal communities or xe2x80x9calgal turfxe2x80x9d and its uses continue and are well-known and reported in patents and literature. By way of background, see U.S. Pat. No. 4,333,263 to Adey; U.S. Pat. No. 4,966,096 to Adey; U.S. Pat. No. 5,097,795 to Adey; U.S. Pat. No. 5,778,823 to Adey; U.S. Pat. No. 5,851,398 to Adey; and U.S. Pat. No. 5,715,774 to Adey et al. It should be noted that the foregoing: patents contemplate harvesting algal turf from its growth substrate by means of hand, livestock, fish or machinery. The disclosure and teaching of these patents are incorporated herein by reference in their entirety.
Recently, there has been an increase in aquatic plant based water treatment (xe2x80x9cAPBWTxe2x80x9d) applications, primarily in the production of fish for human consumption and in nutrient based water treatment systems. Specifically, aquatic plant based water treatment is a mechanism to address non-point source (NPS) pollution such as nutrient pollutants. If the design and operation of constructed commercial sized aquaculture based facilities is to become economically viable, an improved mechanism to manage aquatic plant biomass is necessary.
The major challenges for water treatment technologies employing aquatic plant systems is accessing the plants, efficiently and economically harvesting and collecting the aquatic biomass, and efficiently and economically processing the harvested aquatic biomass.
Two critical items govern the potential value of the aquatic plant biomass generated from water treatment systems. The cost of production and the quality of the product produced. As the plant tissue of an aquatic plant is typically 95% moisture, the total weight of the wet plant tissue is significantly greater than that of terrestrial crops on an equivalent dry weight basis. Accordingly, handling strategies for harvested aquatic plant biomass are critical to the economic cost of handling the biomass.
Harvesting of algal biomass from an ATS, or biomass management, is critical to the sustained performance of an ATS. Harvesting of algal biomass from an ATS occurs on a regular basis, preferably every seven to twenty-one days. Therefore, it is of paramount importance that the biomass management be efficient and cost effective.
Prior art methods for harvesting aquatic plants in natural open waters systems have focused largely on self-propelled floating harvest devices. Severed or collected plant material is either left floating in the water, chopped and left floating in the water, transported to shore by barge or floating in bales, transported by helicopter, or chopped plant material may be pumped as a slurry to a land-based receiving station. Prior art methods for harvesting aquatic plants in natural open water systems have not been employed in the management of aquatic plants within constructed water treatment systems as the harvest strategies are expensive, thereby driving up the cost of the water treatment technology to unacceptable levels. Aquatic plant harvest strategies employed in constructed water treatment systems reflect continuing attempts to improve harvesting efficiency.
There presently exists several apparatus and methods to harvest algal communities. Early methods of harvesting ATS, usually in small scale installations, included hand harvesting which entailed simply scraping algae off the growth substrate. Specifically, the growth substrate or screens were harvested by physically removing the screen from the scrubber and placing it on an inclined easel. Biomass was removed from the screen by scraping with a moderately sharp implement such as piece of hard polystyrene plastic. Scraped biomass was collected in a strainer and de-watered. Difficulties with a hand scraping approach are two-fold. First, depending upon the size of the ATS, it may be difficult to access all portions of the algal turf. Secondly, harvesting via scraping often incompletely removes portions of the algae and allows dislodged algae fragments to settle within the ATS or otherwise not be collected. Incomplete collection of aquatic biomass may permit the release of nutrients which were taken up by the attached algal communities.
In order to expedite harvesting, approaches utilizing vacuum equipment have been utilized. On a small scale, variations of xe2x80x9cshop vacsxe2x80x9d have been utilized to vacuum biomass directly from the ATS growth substrate. For large-scale installations, heavy vacuum equipment designed to vacuum the floway has been utilized. A vacuum unit, either tractor pulled or self-propelled, is typically land based and gains right of entry to the ATS via an access road or floway. However, heavy vacuum equipment has significant operation costs when applied to a large scale ATS system.
Other algal turf harvest systems have included structured floways requiring perimeter wall or curbs employed for retaining water in the floway and facilitating movement of the harvest equipment that is too heavy to travel on the synthetic membrane lined ATS.
Continuing efforts are being made to improve ATS and harvesting of algal communities. By way of example, note U.S. Pat. Nos. 5,846,423; 5,591,341; 5,573,669 and 5,527,456 to Jensen. U.S. Pat. No. 5,846,423 discloses a method for purifying water which requires that the sides of the floway be bounded by a pair of curbs disposed in a spaced-apart parallel relationship. Algal turf is harvested by means of a wheeled harvester disposed to roll along the curbs. A harvesting barge is also contemplated to collect, store and transport harvested algal turf slurry as well as relocate the harvester from floway to floway. See also U.S. Pat. Nos. 5,573,669 and 5,527,456 which are related U.S. patents.
U.S. Pat. No. 5,591,341 discloses a conical floway culture system which contemplates harvesting through use of an angled plowing system having a notched, fixed or rotating scraper whereby harvested algal turf is pushed, thereby increasing the possibility of damage to the culture system.
The disclosure and teaching of these patents are incorporated herein by reference in their entirety.
Therefore, it is an object of this invention to provide an improvement which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of aquatic biomass management art.
Another object of this invention is to provide a harvest apparatus and method that will allow for the economical harvesting of ATS within a large-scale commercial system.
Another object of this invention is to provide an apparatus and method which permits the collection of algal biomass which continuously sloughs from the ATS for processing, thereby improving treatment capacity and effluent quality.
Another object of this invention is to provide an apparatus and method for harvesting and collecting algal biomass which minimizes the need for heavy equipment for the harvesting and transport of algal biomass.
The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.
For the purpose of summarizing this invention, this invention comprises an apparatus and method for harvesting and collecting aquatic plant biomass, and more particularly, to a system and method for harvesting attached algal communities or algal turf whereby water is utilized to transport algal biomass to a central collection location. As used herein, attached algal communities shall mean broadly algal turf or any cultivated algal communities which may be present within an algal turf scrubber (ATS).
Additionally, the apparatus and method of the present invention is drawn to a gathering means whereby algal turf or biomass is severed from the ATS and transferred via a towing means, instead of pushing, thereby reducing potential damage to the ATS. In a preferred embodiment, a weighted harvest drag is dragged over the ATS floway. Severed algal biomass is transferred to a conveyance system that preferably comprises one or more flumes where it is conveyed by a water medium to a central harvest station.
In the apparatus and method of the present invention, a conveyance system via an effluent flume receives algal biomass that is introduced during events via the gathering means as well as algal biomass that is introduced continuously as algal biomass is dislodged or sloughed from the ATS. Harvested and sloughed algal biomass is conveyed by water via the conveyance system (e.g. transport flume) to a central harvesting station. In a preferred embodiment, the collected biomass comprising both harvested and sloughed biomass is removed from the conveyance system water medium by means of a self-cleaning bar screen.
In a preferred embodiment, the conveyance system water medium is the effluent from the ATS; however, the conveyance system water medium may also include water from other sources.
Lastly, the apparatus and method of the present invention is drawn to an ATS having a floway system which does not require lateral perimeter curbs nor restrictions on size dimensions. In a preferred embodiment of the present invention, the ATS is constructed without curbing, and thus without distinct separated floways, thereby reducing ATS construction and maintenance costs and eliminating obstructions for the gathering means.
The foregoing has outlined rather broadly the more pertinent and important features of the present invention in order that the detailed description of the invention that follows may be better understood so that the present contribution to the art can be more fully appreciated. Additional features of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.